This invention is concerned with the production of rubber tubing from latex using an improved extrusion apparatus. Tubing made in such apparatus has a variety of applications, for example in the production of catheters and other tubing for medical use. Different forms of apparatus can be used to produce large diameter tubing which can be formed into elastic bands or rubber thread, to produce single or multiple bore tubing having a wide range of diameters including capillary tubing, and to produce tubing having complex profile from solid or foamed rubber.
The production of rubber tubing from latex by extrusion under gravity is well known. Usually a prevulcanized or post vulcanizable heat sensitive latex compound is used and is delivered under gravity from a constant head storage tank device through a glass head to the annular space between two concentric glass tubes where it comes into contact with a heated zone and forms a solid wet gel which is extruded from the lower extremities of the tubes. The wet gelled tubing is passed into a leaching tank and thence through the usual drying and, if necessary, vulcanization stages. Care must be taken in handling such tubing to prevent self-adhesion. The prevention of self-adhesion is assisted by halogenation of both the outer surface and bore of the tubing or by the application of a suitable lubricant.
It is found to be essential to have the tubes of the extrusion apparatus concentric, otherwise the wet gel is prevented from flowing through the lower portion of the tubes under gravitational pressure.
A disadvantage of the type of glass apparatus currently used is that the glass tubes are attached by fusion to a standard cone and socket ground glass joint. This almost invariably leads to distortion. It is consequently very difficult to obtain concentricity of the two tubes, the achievement of an acceptable result being usually dependent upon success in matching a pair of tubes, which is tedious. Furthermore, the tubes themselves are of standard borosilicate glass with variable bore size and wall thickness; thus it is very difficult to maintain concentricity along the length of the tube.